I've never heard of anti-virus interfering with in-browser JavaScript in that way. My best guess would be that they have their virus scanner running at a very aggressive security level.

The easiest options, in terms of amount of work required to address this issue would be:

Recommend your users lower their security settings

See if they can whitelist your site so the application will work correctly

Recommend a browser other than Internet Explorer, or suggest they install Chrome Frame

Of course, if these are not feasible options, you may have to go with a more simplistic approach to using JavaScript on your page. Instead of requiring JavaScript on the site, use it to enhance the site and make features easier to use.

To do this, you would have to make everything on your site work with JavaScript disabled. Have everything perform POSTs to the server for processing. JavaScript would sit on top of all of this to enhance the experience for users who have JavaScript working. In this scenario, things like anti-virus blocking click events on anchor links would end up with a submission to the server.